Machine-Type Communication (MTC), which is a new communication idea, is intended to integrate a number of different types of communication technologies together, e.g., machine-to-machine communication, machine controlled communication, human-to-machine interactive communication, mobile Internet communication, etc., to thereby develop social production and life styles. As expected, human-to-human communication services will account for only one third of the terminal markets in the future, whereas a larger amount of communication will emerge as MTC communication services. Sometimes MTC communication is also referred to as Machine-to-Machine (M2M) communication or the Internet of Things.
An existing mobile communication network is designed, for example, the capacity of the network is determined, etc., for human-to-human communication. If the mobile communication network is intended to support MTC communication, then the mechanism of the mobile communication system needs to be optimized according to the characteristics of MTC communication, so that MTC communication can be better performed with a minor or no influence upon traditional human-to-human communication.
An important issue of power saving needs to be considered in an MTC communication scenario. In some scenarios, the lifetime of an MTC device is determined directly by the lifetime of a battery, for example, an MTC device for tracking an animal or an MTC device for hydrologic supervision, for both of which it is nearly impossible to replace their batteries, so the MTC device is required to have an extremely low power consumption.
From the perspective of the radio network side, there are two states, i.e., the Radio Resource Control (RRC)_connected state and the RRC_idle state, of a UE in a Long Term Evolution (LTE) system. There are five states, i.e., a state where a dedicated channel is established (cell_dch), a state where a forward access channel is established (cell_fach), a state where a cell is updated periodically (cell_pch), a state where a registration area is updated periodically (ura_pch), and an idle state, of a UE in a Universal Mobile Telecommunication System (UMTS), where cell_dch, cell_fach and cell_pch and ura_pch states belong to the RRC_connected state, and only the UE in the RRC_connected state can transmit uplink data. Once the transmission of data by the UE is completed, the network releases the RRC connection of the UE in an RRC Connection Release message upon monitoring that the UE has no data transmitted for a long period of time, so that the UE enters the RRC_idle state.
The UE in the idle state primarily operates to monitor paging by the network side. In order to save power, the UE generally monitors paging in a DRX mode in which the UE receives in only one sub-frame (10 ms) in each paging cycle but does not receive for the remaining period of time in the paging cycle, particularly as illustrated in FIG. 1.
In the UMTS system, the length of a DRX cycle configured at the network side at present is at most 29 radio frames (i.e. 5120 ms), that is, for DRX in the UMTS system, the UE enables a receiver at most once every 5120 ms to receive a paging instruction message, and possibly a paging message, of the network side, but disables the receiver for the remaining period of time for the purpose of saving power. The longest DRX cycle configured at the network side at present in the LTE system is 2560 ms.
There are possibly two DRX lengths configured for the UE in both the UMTS system and the LTE system. One of the DRX lengths is configured by a Radio Network Controller (RNC)/evolved Node B (eNB) in a System Information Block (SIB) message and can be referred to a default length, which is applicable to all of UEs camping on in the cell; and the other DRX length is negotiated about by a Core Network (CN) entity and the UE in a Non-Access Stratum (NAS) procedure and can be referred to a UE specific DRX, which is only applicable to a single UE. The latter DRX is unknown to the RNC/eNB in a negotiation procedure. The UE monitors a paging message at the shorter one of the two DRX cycles available.
For a paging procedure, the CN entity initiates the paging, and a paging message is firstly transmitted to the RNC (in the UMTS)/eNB (in the LTE system), particularly as illustrated in FIG. 2 and FIG. 3. As illustrated in FIG. 2 and FIG. 3, the paging message carries UE specific DRX configuration. In the UTSM system, the RNC will transmit the paging message via an air interface (i.e., an Iu interface) using a DRX parameter configured in the paging message. In the LTE system, the eNB will compare the DRX parameter configured in the paging message with a DRX parameter configured in a system message and transmit the paging message in the shorter one of the DRX cycles.
In the LTE system, in order to save energy consumption of the UE and to prolong a service period of time of the battery in the UE, the DRX operating mode in the connected state (i.e., the RRC_connected state) is introduced to the LTE to allow the UE to monitor a control channel discontinuously. The DRX operating mode in the connected state includes an active time period and an inactive time period, where the UE needs to monitor a Physical Downlink Control Channel (PDCCH), to receive and send data, and to transmit signaling, in the active time period; and the UE disables a radio frequency unit in the inactive time period to reduce an unnecessary power overhead. The DRX cycle is temporally divided to be in two states, particularly as illustrated in FIG. 4.
Since various services of a user are activated in different levels, for the activation levels for different services, different DRX cycles need to be configured, so long and short cycles are designed for the DRX operating mode in the connected state, where the lengths of the long DRX cycle and the short DRX cycle are configured according to the activation characteristics of the different services of the UE. The length of the long DRX cycle is configured in an RRC message and ranges from 10 to 2560 sub-frames; and the length of the short DRX cycle is configured in an RRC message and ranges from 2 to 640 sub-frames.
The starting position of DRX is the starting point of the “on” state in the DRX cycle, and when the UE will be awoken to monitor a control channel is determined by the starting point of DRX. The UE can be notified explicitly of the offset of a DRX starting point via RRC signaling at the starting point of DRX.
In the UMTS system, the DRX mechanism is introduced to both the cell_fach state and the cell_pch state, and the long and short cycles are applied to both of the states; and the length of the long DRX cycle in both of the states is at most 5120 ms, and the starting point of the “on” state in the DRX cycle is determined similarly to the LTE system.
In the system, the length of the cycle at which a System Frame Number (SFN) is updated (also referred to as an SFN cycle) is 10.24 s, and there are 1024 radio frames, numbered from 0 to 1023, in an SFN cycle, each of which has a length of 10 ms. In the UMTS system, the length of the SFN cycle is 40.96 s including 4096 radio frames, numbered from 0 to 4095, each of which has a length of 10 ms.
For some MTC terminal, a longer DRX cycle needs to be applied for higher power-saving performance; and correspondingly the DRX cycle specified in the existing protocol (e.g., at most 2.56 seconds in the LTE system, and 5.12 seconds in the UMTS) needs to be extended to an order of a minute and even an hour. However if the DRX cycle is extended, then if the extended DRX cycle is longer than the SFN cycle (10.24 s), then the UE can not calculate an accurate active time in the existing approaches because the active time calculated as in the existing approaches lies in the same SFN cycle so that the UE can not be awoken timely at the corresponding active time to receive a message and data transmitted by the network side, thus resulting in a loss of information and consequently degrading seriously the Quality of Service (QoS) of the UE.